I have a female in the 400 g range that eats 100 g rats. Evidently the fro-ro vendor sites consider that a medium, to me they're on the small side (rat-wise, anyway). That is plenty big for the snake & leaves a pretty good bulge in her, but I tend to feed younger animals bigger meals & back them off a bit when they get older.
YMMV...erring on the smaller side isn't going to hurt anything.
K~